ACCEL | In recent years, major studies have been reported, advancing our knowledge of the natural history of bradyarrhythmias and tachyarrhythmias, which may be treated optimally with device therapy. There have also been major advances in the technology of devices that can delay and even prevent morbidity and mortality from arrhythmias and heart failure (HF).

Pacing was once a fairly straightforward technology. Today, once the decision has been made to implant a pacemaker in a given patient, the clinician must decide among a large number of available pacemaker generators and leads. Generator choices include single- versus dual-chamber versus biventricular devices, unipolar versus bipolar pacing/sensing configuration, presence and type of sensor for rate response, and advanced features such as automatic capture verification, atrial therapies, size, and battery capacity. (The TABLE summarizes the appropriateness of different pacemakers for the most commonly encountered indications for pacing.)

An important challenge for the physician in selecting a pacemaker system for a given patient is to anticipate the progression of abnormalities associated with the need for a pacemaker in the first place in order to a select a system for the present that will best accommodate these developments later.

Thus, current guidelines state that it is reasonable to select a pacemaker with more extensive capabilities than needed at the time of implantation but that may prove useful in the future.¹ Some patients with sinus node dysfunction and paroxysmal AF, for example, may develop atrioventricular block in the future (as a result of natural progression of disease, drug therapy, or catheter ablation) and may ultimately benefit from a dual-chamber pacemaker with mode-switching capability.

Similarly, when pacemaker implantation is indicated, the guidelines state that consideration should be given to implantation of a more capable device if it is thought likely that the patient will qualify for the latter within a short time period. More “capable” devices include CRT, pacing but not defibrillation capability (CRT-P), or CRT with defibrillation capability (CRT-D).

For example, the guidelines cite a patient who requires a pacemaker for heart block that occurs in the setting of MI who also has an extremely low LVEF, who may be best served by initial implantation of an ICD rather than a pacemaker. In such cases, guidelines state that the advantage of avoiding a second upgrade procedure should be balanced against the uncertainty regarding the ultimate need for the more capable device.

There is a role for CRT-P in some patients, especially those who wish to enhance their QOL without defibrillation backup. The guidelines note that elderly patients with important comorbidities are such individuals. Notably, there is an important survival benefit from CRT-P alone.

Updated Guidelines

Previously, the only Class I recommendation for CRT was in patients with relatively severe symptoms (NYHA functional class III or IV HF) accompanied by sinus rhythm, LVEF = 35%, a QRS duration = 0.12 second. For the updated guidelines,1 this Class I indication was expanded to patients with NYHA Class II, sending the clear message that CRT “is indicated” for a population with milder symptoms.

Specifically, updates to guideline clinical recommendations included:

Limitation of the Class I recommendation to patients with QRS duration = 150 milliseconds.

Limitation of the Class I indication to patients with left bundle-branch block (LBBB) pattern.

Expansion of Class I indication to NYHA class II (and with LBBB with QRS duration = 150 ms).

The addition of a Class IIb (may be useful) recommendation for patients who have LVEF = 30%, ischemic etiology of HF, sinus rhythm, LBBB with a QRS duration = 150 ms, and NYHA class I symptoms.

A further major expansion of the indication for CRT–the first time ever in patients with NYHA class I symptoms–is provided with a recommendation Class IIb (“may be considered”). This is limited to patients with relatively severe cardiomyopathy (LVEF = 30%) due to ischemia, LBBB, and QRS duration = 150 ms, but expands the option of CRT to patients who previously would not have been considered candidates.

Men and Women

There is a significant underutilization of implantable cardioverter-defibrillators and CRT among women compared to men. However, women do not seem to benefit from primary prevention ICD therapy to the same extent as men.

Kristen K. Patton, MD, and colleagues have reported that women with HF have a lower mortality than men, and fewer of those deaths are sudden throughout a spectrum of all-cause mortality risk.² The data support the possibility that sex differences in ICD benefit may exist.

One meta-analysis revealed no statistically significant decrease in all-cause mortality in women with heart failure who received ICDs (hazard ratio: 1.01).³ On the other hand, women appear to have a better response than men to CRT therapy in terms of reduced numbers of hospitalizations and more robust reverse ventricular remodeling. Importantly, the differences are not explained by differences in baseline characteristics.⁴

Indeed, in terms of magnitude of benefit from CRT, the greatest benefit is seen for females, wider QRS, LBBB, and nonischemic cardiomyopathy. Intermediate benefit is seen among males and individuals with ischemic cardiomyopathy, while the lowest benefit (nonresponders) have narrower QRS or non-left bundle branch block.

References

1. Tracy CM, Epstein AE, Darbar D, et al. J Am Coll Cardiol. 2013;61:e6-e75.
http://content.onlinejacc.org/article.aspx?articleid=1486116
2. Rho RW, Patton KK, Poole JE, et al. Circulation. 2012;126:2402-7.
3. Ghanbari H, Dalloul G, Hasan R, et al. Arch Intern Med. 2009;169:1500-6.
4. Cheng A, Gold MR, Waggoner AD, et al. Heart Rhythm. 2012;9:736-41.

Keywords: ACC Publications, CardioSource WorldNews

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